LIHU‘E — An international team, including University of Hawai‘i at Manoa researchers, found that human-produced climate change has caused significant variations in day-to-day rainfall fluctuations, exacerbating heavy rainfall and drought events and increasing their severity.
“Climate model projections indicate that warming will intensify rainfall variability and extremes, such as heavy rains and drought conditions, across many regions of the globe,” said Malte Stuecker, study co-author and assistant professor in the UH Manoa School of Ocean and Earth Science and Technology (SOEST).
“However, whether these anthropogenic (human-caused) trends are already visible in present-day rainfall observations has remained a major challenge due to large natural fluctuations in rainfall at regional scales.”
When approaching their study, now published in scientific journal Nature, the team came across two significant hurdles. For one, because rainfall can naturally vary greatly, it’s more difficult to label fluctuations as attributable to climate change. Additionally, the study required extensive use of climate models, or simulations, creating an immense catalog of raw data for the team to analyze.
To alleviate these issues, the team utilized a machine learning approach, allowing artificial intelligence to process the climate model’s results in a fraction of the time it would take to do manually.
The machine learning model parsed through the swath of data, seeking out patterns similar to already-established climate change impacts, like increased temperatures or sea level rise.
In addition to conducting much faster analysis than a human alone, the AI used had been fine-tuned specifically to reveal these patterns, meaning the model could more easily find correlations difficult for human analysts to decipher.
“It sounds fancy — ‘machine learning’ — but it is just a bunch of statistical calculations that’s done by the computer to look at these relationships,” Stuecker said. “So there’s no magic there. It’s just a more complicated, more complex way of doing statistics on large amounts of data and trying to find relationships.”
After taking this data and applying it to real-world rainfall observations, the team uncovered what they had hypothesized. Since the mid 2010s, more than 50 percent of all days showed that human-induced global warming clearly deviated precipitation patterns from what could be expected to naturally occur.
“Our study demonstrates for the first time that the human fingerprint is already visible in daily rainfall variability in the tropical eastern pacific and the mid-latitudes,” said Tim Li, study co-author and SOEST professor. “The increased variability in precipitation due to global warming means that we have a greater risk of heavy rainfall and days without rain in these regions.”
Between increased likelihoods of both heavy rains and extended droughts, Stuecker expressed worry over hazardous conditions becoming more common moving forward.
“If we have more rainfall variability in the winter time, we have these issues with flooding — but also potentially, this could lead to more growth of these invasive grass species that played a large role in the Lahaina Fire,” Stuecker said. “And then the drought conditions are a concern here as well.”
However, Stuecker noted further research is needed to determine what effect these climate change impacts could have on specific areas, islands and communities.
“There’s a lot of really regional climate here,” he said. “And that requires careful study, how these large kinds of patterns really impact the local features.”
“There is little doubt that future warming will exacerbate these trends as these are consistent with projections that we showed in our previous work,” he added. “In addition to reducing CO2 emissions as a mitigation measure, more research is needed to better understand the detailed changes in rainfall extremes on small regional scales — such as here on the islands — to guide local adaptation measures.”
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Jackson Healy, reporter, can be reached at 808-647-4966 or jhealy@thegardenisland.com.
